1. Field of the Invention
This invention relates to a high-precision multiple stage speed reducer that incorporates a two-stage integral epicyclic orbiting rotor having significantly different diameters for each stage.
2. Description of the Related Art
Epicyclic power transmission systems have been known for many years. Important improvements have been made in manufacturing techniques and in the design of the epicyclic units, yet such transmission systems have never reached the breadth of application that was anticipated. One reason for this shortfall is relatively high backlash caused by the build-up of tolerances within the unit. In an effort to minimize the backlash increasingly expensive manufacturing procedures have been used, greatly increasing the costs of the units. Excessive friction also occurs in units that are not manufactured with the greatest precision.
Epicyclic speed reducers using pinion gears orbitally rotating within ring gears have been used for limited applications. For example, such units have been used in hand-driven mechanisms for raising and lowering automobile windows and seats. Such a unit is described in U.S. Patent issued in 1962 to Loutron et al in which a pair of pinion gears of different diameter rotate orbitally within a pair of internal ring gears. Such gear units are not efficient in terms of the amount of torque that can be transmitted. The gears are expensive to make because each tooth of each toothed member must be precisely cut. Such devices can transmit only a limited torque because the only a few of the teeth are engaged at any particular time, and these few teeth must carry the entire transmitted torque. This is a defect that is inherent in the gear type speed reducer. Because of these limitations, such drives were not generally suitable for continuous operation particularly under high speed or heavy load conditions. Later, the teeth of the internal ring gear were replaced by a series of rollers or by a hypotrochoid surface. The pinion gear was replaced by an orbiting rotor having an epitrochoidal outer surface. Developments such as these are illustrated by U.S. Pat. Nos. 4,050,331 to Baren; 4,271,726 to Ryffel; and 4,487,091 to Pierrat.
A major step forward is represented by the disclosure in U.S. Pat. No. 4,584,904 to Distin which discloses a drive system in which a pair of conjugate epitrochoidal and hypotrochoidal surfaces are disposed respectively on driving and driven members, with a number of cylindrical rollers interposed between them. These rollers transmit the torque while remaining at all times engaged with the opposed trochoidal surfaces. When manufactured with sufficient precision, the Distin drive accomplishes intended purpose. However, the cost of manufacturing and assembling the drive with the necessary precision has so far precluded its wide industrial application.